1815 13TH ST SEATTLE CHILDRENS NORTH CLINIC Geotech Report 2022-10-25

Structural Fill Materials Materials used to support structures and placed below sidewalks, roadways and parking areas are classified as structural fill for the purpose of this report. Structural fill material quality varies depending upon its use as described below: 1. As a minimum, structural fill placed in parking areas, to backfill utility trenches and to support foundations should meet the criteria for common borrow as described in Section 9-03.14(3) of the Washington State Department of Transportation (WSDOT) Standard Specifications. Common borrow will be suitable for use as structural fill during dry weather conditions only. If structural fill is placed during wet weather,the structural fill should consist of Type 17 aggregate in conformance with City of Seattle Standard Specification 9-03.16 or gravel borrow as described in Section 9-03.14(1) of the WSDOT Standard Specifications, with the additional restriction that the fines content be limited to no more than 5 percent. 2. Structural fill placed as crushed surfacing base course below sidewalks and pavements should meet the requirements of Type 2 aggregate, City of Seattle Standard Specification 9-03.16 or crushed rock base course conforming to Section 9-03.9(3)of the WSDOT Standard Specifications. 3. Structural fill placed immediately outside below-grade and retaining walls (drainage zone) should consist of gravel backfill for walls in conformance with Mineral Aggregate Type 17 (bank run gravel), City of Seattle Standard Specification 9-03.16, with the exception that the percent passing the U.S. No. 200 sieve is to be less than 3 percent or Section 9-03.12(2)of the WSDOT Standard Specifications. 4. Drain rock placed for footing drains (drainage zone) should consist of Mineral Aggregate Type 22 (3/4-inch crushed gravel) or Type 5 (1-inch washed gravel), City of Seattle Standard Specification 9-03.16, or washed 3/a-inch to No. 8 pea gravel per section 9-03.1(4)C AASHTO Grading No. 8 of the WSDOT Standard Specifications, or conform to Section 9-03.12(4) of the WSDOT Standard Specifications. Use of On-site Soils The subsurface soils(fill and glacially consolidated soils) observed in the explorations generally contain a high percentage of fines(silt)and are moisture-sensitive.These soils generally meet the criteria for common borrow and may be suitable for use as structural fill during dry weather. These soils will generally not be suitable for use during wet weather placement. Fill Placement and Compaction Criteria Structural fill should be mechanically compacted to a firm, non-yielding condition.Structural fill should be placed in loose lifts not exceeding 8 to 12 inches in thickness.Each lift should be conditioned to the proper moisture content and compacted to the specified density before placing subsequent lifts. Structural fill should be compacted to the following criteria: 1. Structural fill in new pavement and roadway areas, including utility trench backfill, should be compacted to 90 percent of the maximum dry density (MDD) estimated in general accordance with ASTM D 1557, except that the upper 2 feet of fill below final subgrade should be compacted to 95 percent of the MDD. 2. Structural fill placed below footings should be compacted to 95 percent of the MDD estimated in general accordance with ASTM D 1557. GEOENGINEERS April 22,2016 Page 10 Fite No.10?38-010-01